Hormonal dependence of human prostate tumors transplantable in nude mice : the importance of low androgen levels in prostate tumor growth

The studies presented in this thesis provide experimental data which could contribute to the discussion on whether adrenal androgens are, directly or indirectly, capable of inducing growth stimulation of human prostate tumor tissue. Hormonal titration experiments were conducted to investigate whether there is a critical androgen level for growth stimulation of human prostate tumors and whether or not this threshold level exceeds the androgen levels found in castrated men (Chapters 5 and 7). Since the adrenals of rodents do not secrete androgens (Chapter 6), castration of the mouse can be regarded as total androgen withdrawal. The effect of adrenal androgens on human prostate tumor growth was studied in PC-82 tumorbearing mice supplemented with adrenal androgens, androstenedione and dehydroepiandrosterone (DHEA) (Chapters 7 and 8). In the general discussion (Chapter 10) an attempt is made to integrate experimental data and the derived ideas presented in this thesis with clinical experience on prostate cancer. Hopefully this thesis will contribute to a better understanding of the mechanisms of androgen regulated growth of human prostatic carcinoma which, together with the outcome of the necessary future experiments with human xenograft models, will result in a more effective treatment of patients with advanced prostatic cancer

Patient-derived xenograft models in cancer research

This series of 12 articles, consisting of 9 original articles and 3 reviews, is presented by international leaders in translational cancer research [...

Novel patient-derived 3D culture models to guide clinical decision-making in prostate cancer

Castration-resistant prostate cancer remains an incurable disease. The unmet clinical need to optimally select individual treatment options, and thereby maximize survival benefit, can be addressed by patient-specific preclinical models. Patient-derived organoids preserve original tumor characteristics and have shown potential for high-throughput assessments and coclinical drug testing, as highlighted for several cancer types in this review. This new patient-derived 3D culture technique and its downstream applications are the subjects of intense investigation in prostate cancer. Although challenges are not trivial, we expect a major impact on prostate cancer research, with a window of opportunities for early bench-to-bedside translation of new drug discoveries and guidance of patient-tailored disease management

Peptide receptor imaging of prostate cancer with radiolabelled bombesin analogues

Prostate Cancer (PC) is a type of cancer that is often diagnosed at very early stages due to improved detection among man in the Western world. Current imaging techniques are not optimal to determine extent of minimal early stage PC even though this is of great clinical importance. Human PC and high-grade PIN have shown high Gastrin-Releasing Peptide Receptor (GRPR) expression, while normal prostate tissue and BPH revealed to be predominantly GRPR-negative. Radiolabelled Gastrin-Releasing Peptide (GRP) or bombesin (BN) analogues targeting the GRPR can be used as non-invasive tools to diagnose, monitor and potentially treat PC. These BN analogues have already proven to be able to image PC in both tumour-bearing mice and clinical patients showing no important side effects. It's desirable that new peptides require fast-track standardised comparative testing in relevant PC models to select the best performing BN analogues for further evaluation in patients. Although knowledge about GRPR expression and development of new BN analogues can be extended, it is time to study performance of BN analogues for peptide receptor based imaging in patients validating results of PC imaging using histopathology as a golden standard

Determination of Ki-67 defined growth fraction by monoclonal antibody MIB- I in formalin-fixed, paraffin-embedded prostatic cancer tissues

The applicability of MIB‐1, a monoclonal antibody directed against the Ki‐67 antigen, was studied in the PC‐82 and LNCaP prostatic tumor models at various levels of proliferative activity. Statistically significant correlations were found in LNCaP cultures between Ki‐67 and MIB‐1 scores (r = 0.84, P < 0.001), and in PC‐82 tumors between MIB‐1 scores and paraffin tissue Ki‐67 (pKi‐67) (r = 0.90, P < 0.001), frozen tissue Ki‐67 (fKi‐67) (r = 0.86, P < 0.001), and BrdU uptake (r = 0.70, P < 0.001), respectively. pKi‐67 scores were double the fKi‐67 scores, which may be due to methodological differences. MIB‐1 scores exceeded both the fKi‐67 and pKi‐67 scores. The affinity of MIB‐1 for the antigen is much higher than the affinity of Ki‐67, which may explain the differences. MIB‐1 is a promising means of evaluating the presence of only minute amounts of the Ki‐67 antigen in paraffin‐embedded human tumor material, especially in relatively slowly growing tumors

Effects of low testosterone levels and of adrenal androgens on growth of prostate tumor models in nude mice

Abstract Two transplantable, androgen dependent prostate tumor models of human origin, PC-82 and PC-EW, were used to study the effect of low androgen levels and adrenal androgens on prostate tumor cell proliferation. Tumor load of the PC-82 and PC-EW tumors could be maintained constant when plasma testosterone levels were 0.8 and 0.9 nmol/l, respectively, corresponding with an intratissue 5α-dihydrotestosterone level of 3–4 pmol/g tissue. This critical androgen level for prostate tumor growth stimulation amounted to 2–3 times the castration level and proved to be similar for both tumor models. Relatively high levels of androstenedione resulted in physiological levels of plasma testosterone causing androgen concentrations in PC-82 tumor tissue exceeding the critical level for tumor growth. These results indicate that submaximal suppression of androgens can stop tumor growth in these prostate tumor models

Kinetics of neuroendocrine differentiation in an androgen-dependent human prostate xenograft model

It was previously shown in the PC-295 xenograft that the number of chromogranin A (CgA)-positive neuroendocrine (NE) cells increased after androgen withdrawal. NE cells did not proliferate and differentiated from G0-phase-arrested cells. Here we further characterized NE differentiation, androgen receptor status, and apoptosis-associated Bcl-2 expression in the PC-295 model after androgen withdrawal to assess the origin of NE cells. PC-295 tumor volumes decreased by 50% in 4 days. Intraperitoneal bromodeoxyuridine (BrdU) incorporation and MIB-1 labeling decreased to 0%, and the apoptosis was maximal at day 4. Androgen receptor expression and prostate-specific antigen (PSA) serum levels decreased rapidly within 2 days. The number of NE cells increased 6-fold at day 4 and 30-fold at day 7. Five and ten percent of the CgA-positive cells were BrdU positive after continuous BrdU labeling for 2 and 4 days, respectively. However, no MIB-1 expression was observed in CgA-positive cells. NE cells expressed the regulated secretory pathway marker secretogranin III but were negative for androgen receptor and Bcl-2. Bcl-2 expression did increase in the non-NE tumor cells. In conclusion, androgen withdrawal leads to a rapid PC-295 tumor regression and a proliferation-independent induction of NE differentiation. The strictly androgen-independent NE cells that were still present after 21 days differentiated mainly from G0-phase-arrested cells

Characterization of a zinc-finger protein and its association with apoptosis in prostate cancer cells

BACKGROUND: The transition from androgen-dependent to androgen-independent prostate cancer is not fully understood but appears to involve multiple genetic changes. We have identified a gene, GC79, that is more highly expressed in androgen-dependent LNCaP-FGC human prostate cancer cells than in androgen-independent LNCaP-LNO human prostate cancer cells. Physiologic levels (0.1 nM:) of androgens repress expression of GC79 messenger RNA (mRNA) in LNCaP-FGC cells. To determine the role of GC79, we cloned its complementary DNA (cDNA) and functionally characterized its product. METHODS: The differentially expressed GC79 gene was cloned from human prostate cDNA libraries, sequenced, and transfected into mammalian cells to study its function. Expression of GC79 was analyzed in various adult and fetal human tissues and in prostate glands of castrated rats. The association of GC79 expression and apoptosis was investigated in COS-1 and LNCaP cells transfected with GC79 cDNA. All statistical tests are two-sided. RESULTS: Sequence analysis indicates that GC79 encodes a large, complex, multitype zinc-finger protein, containing nine C(2)H(2)-type zinc-finger domains, a cysteine-rich region, and a GATA C(4)-type zinc-finger domain. Castration-induced androgen withdrawal increased the expression of GC79 mRNA in the regressing rat ventral prostate, suggesting that the expression of GC79 mRNA is associated with the process of apoptotic cell death in the rat ventral prostate. Transfection and induction of GC79 cDNA in both COS-1 and LNCaP prostate cancer cells led to an apoptotic index that was eightfold higher (P:<.001, two-sided Student's t test) than that observed in uninduced transfected cells. CONCLUSIONS: We have cloned an androgen-repressible gene, GC79, that is potentially involved in apoptosis. This finding may have implications for the development of androgen-independent prostate cancer and, ultimately, for the treatment of prostate cancer

Testosterone Diminishes Cabazitaxel Efficacy and Intratumoral Accumulation in a Prostate Cancer Xenograft Model

Inactivation of the androgen receptor (AR) pathway by androgen deprivation therapy (ADT) is the mainstay of (metastatic) prostate cancer therapy. Ultimately, the AR pathway will be re-activated despite castrate levels of circulating androgens. Thereby, maintaining its role even in castration resistant prostate cancer (CRPC). The recent STAMPEDE and CHAARTED trials showed that docetaxel in combination with ADT increased survival in hormone sensitive prostate cancer patients, suggesting cross-talk between AR signaling and chemotherapy efficacy. We hypothesized that a similar interaction may also apply for CRPC that is treated with cabazitaxel. We studied the impact of androgen status on the efficacy, pharmacodynamics and -kinetics of cabazitaxel in a unique and clinically relevant patient derived xenograft model of castration resistant disease. We found that cabazitaxel is highly effective in a castrate setting with strongly reduced AR activation, while tumor growth inhibition by cabazitaxel was completely abolished in the presence of high AR pathway activity. Moreover, additional experiments showed that intratumoral cabazitaxel levels were 3.5 times higher in tumors from castrated mice as compared to tumors from androgen-supplemented animals. We confirmed that cabazitaxel pharmacokinetics were not affected by testosterone, suggesting that androgen status might influence cabazitaxel tumor uptake directly. This study reveals the impact of androgen status on cabazitaxel efficacy and supports the potential of combination of taxane chemotherapeutics with AR axis targeting agents